Separate control line for maintenance of repeaters of a digital subscriber line

ABSTRACT

Digital subscriber line (DSL) system comprising a digital subscriber line access multiplexer (DSLAM,  20 ) having a line trunk unit (LTU,  13 ), a repeater container ( 23 ) containing a repeater ( 16 ) and a customer premises equipment (CPE,  11 ) having a network terminating unit (NTU,  15 ) in which the repeater ( 16 ) connects a line trunk unit ( 13 ) to a network terminating unit ( 15 ) through respective lengths ( 18, 19 ) of a digital subscriber line and in which both the digital subscriber line access multiplexer ( 20 ) and the repeater container ( 23 ) comprise an operation and maintenance unit (OMU,  21, 24 ) which are connected to each other by a line ( 25 ) which is separate from the digital subscriber line for controlling the operation and maintenance of the repeater ( 16 ) or repeaters ( 16 ) of the repeater container ( 23 ) from the digital subscriber line access multiplexer ( 20 ).

The invention relates to a digital subscriber line (DSL) system asdescribed in the preamble of claim 1.

A digital subscriber line system of such type is known from practice.There are several subtypes of a communication type which is known as“Digital Subscriber Line” (DSL) between a central unit or DigitalSubscriber Line Access Multiplexer (DSLAM) having a Line Trunk Unit(LTU) and a subscriber unit or Customer Premises Equipment (CPE) havinga network terminating unit (NTU). Communication through digitalsubscriber line comprises the possibility to be used with twisted copperwire pairs which are presently commonly used for voice basebandcommunication. Asynchronous Digital Subscriber Line (ADSL) communicationallows a download (towards the subscriber) bitrate of 8 Mbit/s and anupload (towards the central unit) bitrate of 1 Mbit/s at the same timethrough a single copper wire pair. Depending on an error rate occurringduring communication the bitrates are adapted below said figures untilan acceptable error rate is obtained. In the central unit and in thesubscriber unit filters are used to combine or separate baseband voicesignals and higher frequency digital data signals. High bitrate DigitalSubscriber Line (HDSL) communication allows a bitrate in both thedownload and upload directions of 2 Mbit/s over two respective copperwire pairs. Said bitrate of 2 Mbit/s is fixed, that is, independent froman error rate occurring during communication. HDSL can be calledsymmetric DSL because of the identical bitrates in both directions.Other symmetric DSL communication types are Symmetrical single pairDigital Subscriber Line (SDSL) and Symmetrical single pair High bitrateDigital Subscriber Line (SHDSL). All types of digital subscriber linecommunication together are indicated by xDSL.

The copper pairs used for XDSL are pairs of a huge cable bundle of many(for example 80) pairs which are used for several types ofcommunication, such as voice and ISDN and, recently, xDSL. In particularISDN and xDSL communications over neighbouring copper pairs carryinghigh frequency signals may adversely effect each other. This may requirethe use of repeaters in copper pairs for symmetric or fixed bitratedigital subscriber line communication (HDSL, SHDSL and SDSL) exceedingspecific error rates or a specific distance between the central unit andthe subscriber unit. Such distance may be for example 3 km. For thisreason a repeater container containing several repeaters is used withone repeater serving a single subscriber line. Usually the repeatercontainer is buried. The repeaters are managed for operations andmaintenance from the central unit through the same copper pair whichthey are serving, thus using the same frequencies as used for the properdata and voice signals between the central unit and the subscriber. Suchtype of management can be called in-band management. In-band managementhas several disadvantages. If a repeater fails it is almost impossibleto detect the problem and to solve it from the central unit. It may evenrequire to dig up the repeater container for a local check. This ofcourse is very time consuming and expensive. A repeater may malfunctionfor several reasons, some of which could be solved by downloading somecontrol data or alternative software into the repeater. However, afailing repeater may not enable such downloading. In addition, though arepeater may seem to fail, in fact it could be working well but one orboth subscriber line lengths to which it is connected is or are causingproblems. The repeater and a subscriber line length may even both causeproblems. Under circumstances it is not possible to detect from thecentral unit which of those are causing problems, making it impossibleto choose and use a proper method for solving the problems from thecentral unit. Again this may require digging up the repeater containerfor a check of the repeater in question and the line lengths connectedtherewith from the container.

It is an object of the invention to solve the drawbacks of the prior artdigital subscriber line system and to increase the quality of service.

To that end a digital subscriber line system according to claim 1 isprovided by the invention.

The system provided by the invention provides out-band management ofoperations and maintenance of several repeaters contained in therepeater container, that is apart from the voice signals and datasignals going through the repeaters, which makes said managementresistant against influences from such signals and malfunction of one ormore repeaters. Communication between the operations and maintenanceunits may need the voice baseband only, so that the copper pairconnecting the operations and maintenance units may be any of the bundleit is part of in view of possibly adverse influence from other pairs ofthe bundle.

The invention also provides a method according to claim 6.

The invention will be described below with reference to the encloseddrawings, in which:

FIG. 1 shows a diagram of a digital subscriber line system according tothe prior art;

FIG. 2 shows a diagram of a digital subscriber line system according tothe invention; and

FIG. 3 shows a diagram of a repeater for exemplifying a checkingoperation thereof.

The diagram of the prior art digital subscriber line system shown inFIG. 1 comprises a digital subscriber line access multiplexer (DSLAM)10, one or more customer premises equipment (CPE) 11 and a repeatercontainer 12.

The digital subscriber line access multiplexer 10 comprises for eachdigital subscriber line it is serving a line trunk unit (LTU) 13. Thedigital subscriber line access multiplexer 10 further comprises acentral processing unit (CPU) 14 which controls the operation of theline trunk units 13.

The customer premises equipment 11 comprises a network terminating unit(NTU) 15.

The repeater container 12 contains one or more repeaters or repeaterunits 16.

Dependent on an error rate a line trunk unit 13 can be connecteddirectly to a network terminating unit 15 of a customer premisesequipment 11 by a digital subscriber line 17, which, dependent on thedigital subscriber line type, may consist of one or two twisted copperwire pairs. If required because of the error rate or distances betweenthem a line trunk unit 13 may be connected to a network terminating unit14 through a repeater 16 by respective digital subscriber line lengths18, 19 respectively. As indicated with the lower subscriber line length18 in FIG. 1 a repeater container 12 may serve digital subscriber linesconnected to different digital subscriber line access multiplexers 10,possibly of different central units.

An acceptable length of a digital subscriber line 17 in which norepeater 16 is arranged is, for example, 3 km. Then, the digitalsubscriber line lengths 18, 19 which have a repeater 16 connectedbetween them are also about 3 km at most.

Operation and maintenance of each repeater 16 is carried out by thecentral processing unit 14 of the digital subscriber line accessmultiplexer 10 by communication over the digital subscriber line length18 to which the repeater 16 and the associated line trunk unit 13 areconnected. In case of malfunction of a repeater 16 it will not always bepossible to detect whether a communication problem detected at the sideof the digital subscriber line access multiplexer 10 is caused byfailing of the digital subscriber line lengths 18 and 19 or the repeater16. In addition, the data transferred for the operation and maintenancecontrol of the repeater 16 by the central processing unit 14 may bedisturbed by signals carried over other copper wire pairs than those ofline lengths 18, 19 and, dependent on the quality of communication,disturbed by signals supplied by the line trunk unit 13 to digitalsubscriber line length 18 or by the network terminating unit 15 of theassociated customer premises equipment 11 to digital subscriber linelength 19. This makes proper analysis of a communication path comprisinga repeater 16 and digital subscriber line lengths 18 and 19 difficult,if not impossible. In addition, it may prevent software being downloadedfrom the digital subscriber line access multiplexer 10 to cure any ofsaid problems, for example by updating software contained in therepeater 16 for its operation and maintenance.

The diagram of the digital subscriber line system according to theinvention shown in FIG. 2 differs from the system shown in FIG. 1 bythat the digital subscriber line access multiplexer 20 of FIG. 2comprises in addition with respect to multiplexer 10 of FIG. 1 a firstoperations and maintenance unit (OMU) 21 and in that the repeatercontainer 23 of FIG. 2 comprises in addition with respect to container12 of FIG. 1 a second operations and maintenance unit (OMU) 24. Thefirst operations and maintenance unit 21 is connected to the centralprocessing unit 14. The second operations and maintenance unit 24 isconnected to one or more repeaters 16 of the repeater container 23. Thefirst and second operations and maintenance units 21, 24 are connectedto each other by a copper wire pair 25 which is intended to carrycontrol data signals for use by the operations and maintenance units 21,24 only. The remaining components of the systems of FIG. 1 and 2 maybasically be identical.

With the system shown in FIG. 2 analysis of the digital subscriber linelengths 18, 19 and the repeaters 16 is possible with very little chanceof being disturbed by signals originating from other copper wire pairswhich may be in use for a low speed connection over longer distance.Such analysis may even be carried out frequently, more often then withthe system of FIG. 1, without taking proper data transfer capacity fromthe digital subscriber lines 18, 19 which the repeaters 16 are serving.Software can be downloaded from the first operations and maintenanceunit 21 safely over copper wire pair 25 to the second operations andmaintenance unit 24, possibly for updating its software for theoperation and maintenance of the repeaters 16.

As shown diagrammatically in FIG. 3 the operations and maintenance unit24 of a repeater container 23 may control a repeater 16 such that itmakes a short connection, indicated by arrow 31 between two copper wirepairs 32, 33 of a digital subscriber line length 18 as close as possibleto terminals of the repeater 16 to which said pairs 32, 33 areconnected. Similarly, the operations and maintenance unit 24 of therepeater container 23 may make a short connection, indicated by arrow 35between copper wire pairs 36, 37 of the other digital subscriber linelength 19 as close as possible to terminals of the repeater 16 to whichsaid pairs 36 and 37 are connected. By selectively applying such shortconnections 31, 35 it is possible to identify which of the digitalsubscriber line lengths 18, 19 or the repeater 16 is possiblymalfunctioning. With the prior art system shown in FIG. 1 making suchshort connection 31 was impossible to make if the digital subscriberline length 18 or the repeater 16 itself failed either physically or bydistortion of the signals which were carried. The same applies for thepossibility to monitor failing of a remote power feeding the repeaters16 of the repeater container 23.

In case that one digital subscriber line length 18, 19 fails, forexample if it is physically disrupted, a loss of incoming signal (LIS)or loss of outgoing signal (LOS) can be generated by the operations andmaintenance unit 24 of the repeater container 23 and then transmitted tothe operations and maintenance unit 21 of the digital subscriber lineaccess multiplexer 20 to take adequate action.

It is observed that with the prior art system shown in FIG. 1 it wasonly possible to detect failure of line length 19 or a combination ofline lengths 18 and 19. With the system according to the invention it ispossible to monitor and manage each line length 18, 19 independent fromeach other.

In addition it is observed that the invention can be applied also for aseries connection of several line lengths (each at most 3 km, forexample) and repeaters 16 of different container repeaters 23 inbetween. The same applies for a series connection of control lines andoperations and maintenance units 24 of different container repeaters 23.This will still allow monitoring and causing any failures which weremanageable in a simple system as illustrated in FIG. 2. This would bevirtually impossible with a prior system having series connections ofline lengths and repeaters in between.

1. Digital subscriber line system (DSL) comprising a digital subscriberline access multiplexer (DSLAM, 20) having a line trunk unit (LTU, 13),a repeater container (23), which contains a repeater (16) and a customerpremises equipment (CPE, 11) having a network terminating unit (NTU,15), in which lengths (18, 19) of a subscriber line connect the repeaterto the line trunk unit (LTU, 13) and to the network terminating unit(NTU, 15) respectively, characterized in that the digital line accessmultiplexer (DSLAM, 20) comprises a first operations and maintenanceunit (OMU, 21) and the repeater container (23) comprises a secondoperations and maintenance unit (OMU, 24) which is connected to therepeater (16), the first and second operations and maintenance units areconnected by a control line (25) which is apart from the digitalsubscriber line, and the operations and maintenance units being suitableto operate and maintain the repeater in co-operation through controlline (25).
 2. Digital subscriber line system according to claim 1,characterized in that the control line (25) is of a type of a length ofsubscriber line.
 3. Digital subscriber line system according to claim 1or 2, characterized in that the line trunk unit (13) and the networkterminating unit (15) are connected by a series of line lengths andrepeaters (16) of different repeater containers (23) in between, and thesecond operations and maintenance units (24) of the different repeatercontainers are connected to at least one first operations andmaintenance unit (21) of the digital subscriber line access multiplexer(20).
 4. Digital subscriber line system according to claim 3,characterized in that the second operations and maintenance units (24)are connected to the at least one first operations and maintenance unit(21) by individual control lines (25).
 5. Digital subscriber line systemaccording to claim 3, characterized in that the second operations andmaintenance units (24) are connected in series and to one firstoperations and maintenance unit (21) by control lines (25) in between.6. Method for operating and managing a repeater (16) for repeating adigital subscriber line signal which is supplied to it and which iscommunicated through it between a digital subscriber line accessmultiplexer (20) and a customer premises equipment (CPE, 11), in whichcontrol signals to operate and manage the repeater (16) are communicatedbetween the repeater (16) and a processing unit (14) of the multiplexer(20), characterized in that control signals from and to the multiplexer(20) are communicated over a communication path which is distinct from acommunication path for the digital subscriber line signal.
 7. Methodaccording to claim 6, characterized in that the processing unit (14)delegates generating, transmitting, receiving and processing of controlsignals to a first operations and managing unit (21) of the multiplexer(20).
 8. Method according to claim 6 or 7, characterized in that therepeater (16) delegates generating, transmitting, receiving andprocessing of control signals to a second operations and managing unit(24).
 9. Method according to one of the claims 6-8, characterized inthat control signals from and to the multiplexer (20) and a plurality ofthe repeaters (16) are communicated over different communication pathsbetween the multiplexer (20) and each repeater (16) respectively. 10.Method according to claim 9, characterized in that the control signalsto and from different ones of the repeaters are communicated to and fromthe multiplexer (20) over a common communication path.